Adsorption of 4^4He on a single C60_{60}

The adsorption of $^4$He inside and outside a single fullerene C$_{60}$ is studied. A physisorption potential is proposed. The energetics and structural features of C$_{60}$-$^4$He$_N$ clusters are investigated. Particular attention is paid to the growth of the highly pronounced layered density profile. The evolution towards bulk liquid and surface thickness at the free interface are discussed.Comment: 7 pages (TeX), 7 figure

Density profiles of Ar adsorbed in slits of CO_2: spontaneous symmetry breaking

A recently reported symmetry breaking of density profiles of fluid argon confined by two parallel solid walls of carbon dioxide is studied. The calculations are performed in the framework of a nonlocal density functional theory. It is shown that the existence of such asymmetrical solutions is restricted to a special choice for the adsorption potential, where the attraction of the solid-fluid interaction is reduced by the introduction of a hard-wall repulsion. The behavior as a function of the slit's width is also discussed. All the results are placed in the context of the current knowledge on this matter.Comment: Text plus 8 figure

Induced scalar interaction in the analysis of superallowed fermi β transitions

Nuclear Structure superallowed Fermi/3 transitions; derivation of the coupling constant for the induced scalar interaction fs from experimental data. Very recent works reported a significant improvement in the consistency of Yt values for superallowed Fermi/3-decays. This fact led us to investigate some aspects which are not usually tackled in a study of this kind of transition. In a recent paper we suggested that an upper limit for the coupling constant fs for the induced scalar interaction can be derived analyzing superallowed Fermi /3-transitions. In the present work we revise and improve the method for the determination of fs. The result obtained, fs/fv = (-0.4 __ 1.4) x 10- 3, agrees with the prediction of the CVC theory.Facultad de Ciencias Exacta

The decay of the T=1 isospin triplet in A=12 systems: II. The induced interactions in the anisotropy of beta-rays

Nuclear Structure: calculation of the asymmetry α∓ of β rays emitted from polarized 12B and 12N nuclei. Comparison with experimental values. Formulae for the asymmetry parameters α∓ of β rays emitted from polarized nuctei is derived using the formalism developed by Behrens-Biihring. The induced interactions are studied in detail. It is demonstrated that the expressions for α∓ are independent of the induced pseudoscalar interaction. It was found that the corrections to the lowest order approximation are small. Experimental data of the Louvain and Osaka laboratories are analyzed. We should point out that the data of the asymmetry of the β decay of 12B obtained in these two laboratories are quite different. Although the data reported by the Osaka Group require the existence of the induced pseudotensor (IPT) interaction as it, has also been stated by other authors, if we combine data of 12N from Osaka and of lZB from Lauvain such experimental results can be understood without including the IPT interaction. Thus, we found some evidence that the IPT interaction could be not necessary to explain the asymmetries in the decay of members of the A = 12 system.Facultad de Ciencias Exacta

Full correspondence between asymmetric filling of slits and first-order phase transition lines

Adsorption on single planar walls and filling of slits with identical planar walls are investigated in the frame of the density functional theory. In this sort of slits the external potential is symmetric with respect to its central plane. Calculations were carried out by applying both the canonical and grand canonical ensembles (CE and GCE, respectively). The behavior is analyzed by varying the strength of the adsorbate-substrate attraction, the temperature T, and the coverage Results obtained for physisorption of Xe on alkaline surfaces are reported in the present work. Prewetting (PW) lines and wetting temperatures, Tw, are determined from the analysis of adsorption on single walls. The filling of slits is analyzed for temperatures T Tw. It is found that whenever for a given Xe-substrate combination the adsorption on a single wall exhibits a first-order wetting transition then asymmetric profiles that break the left-right symmetry of the external potential appear in the filling of an equivalent slit. These spontaneously symmetry breaking (SSB) solutions occur in a restricted range of with a T-dependent width. In the case of closed slits analyzed in the CE scheme, the obtained asymmetric profiles exhibit lower Helmholtz free energies than the symmetric species and, therefore, could be stabilized in this geometry. For open slits, the GCE scheme yields all the symmetric and SSB states in the corresponding convex regimes of the free energy. It is shown that both the CE and the GCE frames yield three coexistent states, two symmetric and one asymmetric twofold degenerate. Both a PW line and the related SSB effect terminate at the same temperature. For rather strongly attractive surfaces reentrant SSB states are found at a fixed value of T.Fil: Szybisz, Leszek. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sartarelli, Salvador Andrés. Universidad Nacional de General Sarmiento. Instituto del Desarrollo Humano; Argentin

Surface term for the capillary condensation transitions in a slit geometry

It is shown that a bare simple fluid model (SFM) proposed some years ago for studying adsorption between two semi-infinite solid walls can be improved by modifying the surface term in the grand potential for the film phase. Such a correction substantially improves the agreement between the predictions for phase transitions provided by that SFM and results obtained from calculations carried out for $^4$He with the density-functional method at zero temperature. The corrective term depends on the strength of the adsorption potential and observables of bulk helium.Comment: 4 pages, 1 table and 5 figure

Confinement of Ar between two identical parallel semi-infinite walls

The confinement of Ar in planar slits of two identical parallel semi-infinite walls of alkali metals, alkaline-earth metal Mg, and CO 2 is investigated within the framework of the density functional theory. It is assumed that (1) the fluid atoms interact via a recently proposed effective attractive pair potential with strength, εff, which reproduces the experimental data of the surface tension of the liquid-vapor interface at the bulk coexistence curve, and (2) the adsorption on the walls is described by ab initio potentials characterized by a well depth, Wsf. In this way the systems were studied in the framework of a realistic approach. We found that for small coverages, the slit is always filled by forming two symmetric vapor films, one at each wall. For increasing coverage the behavior depends on the ratio Wsf/εff and the temperature T. In the case of alkali metals, we found at the triple point, Tt, of the adsorbate a regime of average density ρ*av in which the ground state exhibits asymmetric density profiles, leading to the so-called spontaneous symmetry breaking (SSB) effect. The SSB appears at an average density ρ*sb1 and disappears at a higher average density ρ*sb2 . When T is increased, the range of densities ρ*sb1≤ρ*av≤ ρ* sb2 diminishes and eventually the SSB disappears at a critical temperature, Tsb, which coincides with the critical prewetting temperature Tcpw observed in the adsorption on a single wall. For T>Tcpw the slit is filled symmetrically up to the phase transition to capillary condensation. All these features are examined as a function of the strength of the substrate and the width of the slit. Furthermore, no SSB effect was found for Mg and CO2.Fil: Sartarelli, Salvador Andrés. Universidad Nacional de General Sarmiento; ArgentinaFil: Szybisz, Leszek. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Adsorption of fluids on solid surfaces: A route toward very dense layers

Adsorption of Xe on single planar walls is investigated in the frame of a density functional theory. The strength of the adsorbate-substrate attraction is changed by considering surfaces of Cs, Na, Li, and Mg. The behavior is analyzed by varying the temperature T (between the triple point Tt and the critical Tc) and the coverage image. The obtained adsorption isotherms exhibit a variety of wetting situations. Density profiles are reported. It is shown that for strongly attractive surfaces the adsorbed liquid becomes very dense reaching densities characteristic of solids.Fil: Sartarelli, Salvador Andrés. Universidad Nacional de General Sarmiento. Instituto del Desarrollo Humano; ArgentinaFil: Szybisz, Leszek. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentin